1. Technical Field
The present invention relates to a radio base station and a mobile station.
2. Background Art
In the LTE (Long Term Evolution)—Advanced scheme, a physical (PHY) layer, a MAC (Media Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an RRC (Radio Resource Control) layer are provided in a mobile station UE and a radio base station eNB as illustrated in FIG. 5.
The PDCP layer on a transmission side is configured to perform an encryption process and a process for falsification detection on a PDCP-SDU (Service Data Unit) received from the RRC layer using a COUNT value, and transmit a PDCP-PDU (Protocol Data Unit) provided with a PDCP-SN (Sequence Number) as a header to the RLC layer.
Here, the COUNT value includes an HFN (Hyper Frame Number) and the PDCP-SN as illustrated in FIG. 6.
Incidentally, the PDCP-SN has 12 bits and is configured to be incremented each time the PDCP-PDU is generated and transmitted to the RLC layer. The HFN has 20 bits and is configured to be incremented each time the PDCP-SN circulates.
On the other hand, the PDCP layer on a reception side is configured to perform an encryption process and a falsification detection process using a COUNT value.
Furthermore, the PDCP layer on the transmission side can select one out of two kinds, i.e., “Longer-SN” having a 12-bit length and “Shorter-SN” having a 7-bit length as illustrated in FIG. 7 and set up the selected one as the PDCP-SN for a bearer (for example, voice bearer) of RLC-UM (Un-Acknowledged Mode).
Here, the “Longer-SN” has an advantage that tolerance to a packet loss is strong, but has a disadvantage that the overhead becomes large.
On the other hand, the “Shorter-SN” has an advantage that the overhead is small, but has a disadvantage that tolerance to a packet loss is weak.
In general, therefore, it is considered to be preferable to use the “Shorter-SN” for a bearer that requires a high quality such as the voice bearer, from a viewpoint of coverage (viewpoint of overhead).